1. Technical Field
The subject invention relates generally to the field of tube bending and, more particularly, to a novel concentric bore bend die and clamp insert used in a tube bending apparatus.
2. Description of Related Art
The technique of rotary draw tube bending derives its name from the concept of a tube or pipe being clamped, held and rotated around a bend die. During the process, the tube is pulled or drawn forward. As illustrated in FIG. 1, the minimum tools or components required in an apparatus for performing rotary draw tube bending are a clamp die 10, a bend die 12, and a pressure die 14. The bend die 12 is mounted on the center line of rotation of the tube bending apparatus, and the bend die 12 includes a shaped working area and a clamping area 16 with a tube groove extending through both areas. The clamp die 10 is situated opposite to the clamping area 16 on the bend die 12 and is positioned to hold a tube 18 in place against the clamping area 16 during the bending process as the clamp die 10 and the bend die 12 rotate in conjunction along a rotational direction 20. As the bend die 12 is rotated, it pulls the tube 18 to be bent around the bend die 12. The center line radius of the tube 18 being bent is determined by the diameter of the bend die 12. The function of the pressure die 14 is to hold the tube 18 against the bend die 12 and hold back reaction forces during the bending process to create the bend. The bending occurs within a narrow zone just prior to and slightly following the point where the pressure die 14 is tangent to the bend die 12. There are generally two types of pressure dies 14, the static type that remain in a fixed position during the bending process, and the tracking type that move with the material as it is wrapped around the bend die 12.
A rotary draw tube bending apparatus may also include other optional components, such as a wiper die 22 and/or a mandrel (not shown). A wiper die 22 is situated directly opposite to the pressure die 14 in order to prevent the tube 18 from distorting during the bending process. The wiper die 22 is manufactured and fitted to conform with the bend die 12 tube groove and the center line radius of the bend die 12. A mandrel is a component positioned to support the inner diameter of the tube 18 to be bent, where the mandrel also provides a surface to control metal flow in the bend tangent area of the part being bent. The mandrel basically serves to maintain a desired inner diameter of the tube 18 and to keep the tube 18 from flattening out during the bending process. Once the bending procedure is completed, the clamp die 10 and pressure die 14 are returned to their open position, and the bent tube is either moved to the next bend position or removed from the rotary draw tube bending apparatus.
The pressures exerted by the clamp die 10 through the tube 18 on the clamping area 16 of the bend die 12 during the bending process can lead to material failure of the bend die 12 and/or cause excessive wear to occur in the clamping area 16. In order to extend the life of the bend die 12 and to minimize the costs associated with replacing expensive bend die tooling, there have been attempts to position clamp inserts in the clamping area 16 of the bend die 12. Previous clamp insert designs have involved cutting a rectangular cutout region into the clamping area 16 of the bend die 12 and fitting a respectively shaped clamp insert into the rectangular cutout region.
The choice of material selected for constructing bend dies and clamp inserts have presented tool designers with conflicting considerations. Risk of tool failure can occur either i) by breakage if the material is too hard or ii) by rapid wear if the material is too soft. Due to stresses radiating through the clamp insert from the clamped bend tube 18 during the bending process, it has been necessary to make the traditional rectangular clamp inserts to possess a sufficient thickness so as to avoid breakage. Thus, the length of the clamp insert has traditionally been limited by there being a lack of available back up support by the bend die 12 to enable extension of the cutout region and, in turn, allow the clamp insert to extend all the way to tangent of the rotational axis of the bend die 12. These strength limitations further extend to the bend die 12, which must also maintain sufficient thickness on the sides of the rectangular cutout region so as to avoid material failure, breakage, and deflection. Further, there are limitations in the manners in which the clamp insert has traditionally been attached to the bend die 12, which has also led to material failure of the bend die 12.